Generally, a sliding vane type compressor, as shown in FIG. 1, comprises a cylinder 1 having therein a cylindrical space, side walls (not shown in FIG. 1) being fixed to both sides of the cylinder 1, and sealing blade chambers 2a and 2b being defined on opposite sides of the inner space in the cylinder 1, a rotor 3 disposed at the center thereof, vanes 5 being slidably engageable with grooves 4 provided in the rotor 3, suction bores 6a and 6b being formed in the cylinder 1, discharge bores 7a and 7b being formed in the same, communication conduits 8a and 8b communicating with the blade chambers 2a and 2b and the bore 6a and 6b being formed in the cylinder 1, and set screws 9a and 9b being provided at the suction side and those 10a and 10b being provided at the discharge side.
The vanes 5 project outwardly by a centrifugal force as the rotor 3 rotates, so that the outermost ends of vanes 5 slidably move along the inner periphery of cylinder 1, thereby prevent leakage of gas from the compressor.
FIG. 2 is a sectional side view of the compressor, in which reference numeral 11 designates a front plate reference numeral 12 designates a rear plate, reference numeral 13 designates a front casing, reference numeral 14 designates a rotary shaft, reference numeral 15 designates a shell, reference numeral 16 designates an annular suction conduit formed between the front casing 13 and the front plate 11, reference numeral 17 designates a suction piping joint, reference numeral 18 designates a suction conduit shown in broken line, reference 19 designates a disc for a clutch means, and reference numeral 20 designates a pulley for the clutch means.
The compressor, as shown in FIG. 1, having the cylinder 1 with an inner surface non-circular in section, requires a plurality of pairs of suction bores and discharge bores.
The inner surface of cylinder 1 being about elliptic in section, the compressor discharges a refrigerant compressed in the right-hand and left-hand blade chambers 2a and 2b through two discharge bores 7a and 7b into a common space 21 formed of cylinder 1 and shell 15.
Supply of the sucked refrigerant into two blade chambers 2a and 2b is separate from the discharge side and cut off therefrom by use of a construction shown in FIG. 2.
In detail, between the front plate 11 and the front casing 13 is formed the annular suction conduit 16 communicating in common with two suction bores 6a and 6b and the piping joint 17 provided at the front casing 13 connects the conduit 16 with an external refrigerant supply source (an exit of an evaporator).
Such a construction need only provide such one suction and piping joint even in a multilobe type compressor having two or more cylinder chambers.
Such a sliding vane type rotary compressor can be small-sized and simple in construction rather than the reciprocating compressor which is complex in construction and of many parts, thereby having recently been used for the car cooler compressor. The rotary compressor, however, has the following problems in comparison with the reciprocating compressor.
In a case of a car cooler (air conditioner), a driving force is transmitted from an engine to the pulley 20 at the clutch means through a belt to drive rotary shaft 14 of the compressor. Hence, when the sliding vane type compressor is used, its refrigerating capacity rises about linearly in proportion to the rate of rotation of the car engine.
On the other hand, in the case of using the reciprocating compressor, the follow-up property (response) of a suction valve becomes poor during high speed rotation and the compressed gas cannot be fully sucked into the cylinder. As a result, the refrigerating capacity leads to saturation during high speed driving. In brief, while the reciprocating compressor automatically suppresses the refrigerating capacity during the high speed driving, the rotary one does not do so and its efficiency deteriorates as the compression work increases, or is called upon to provide excessive cooling. In order to solve the above problem, the method has hitherto been proposed that a control valve for changing an opening area of communication be provided in the conduits communicating with the suction bores 6a and 6b at the rotary compressor, the opening area being restricted during the high speed rotation to utilize the suction loss for performing capacity control. In this case, however, an extra control valve must be attached, thereby creating the problem that the compressor is more complex in construction and expensive to produce. Another method, which uses a fluid clutch or planetary gears so as not to increase the rate of rotation above a predetermined value, has hitherto been proposed for eliminating the excessive capacity of compressor during the high speed driving.
However, the former method creates a greater energy loss caused by frictional heating between relatively moving surfaces, and the latter method requires the addition of a planetary gear mechanism of many parts so that the compressor is larger in size and configuration, thereby being difficult to put into practical use because the recent demand for energy saving increasingly requires simplification and miniaturization of the compressor.
After detailed research by the inventors of transient phenomena of pressure in the blade chamber in a case of using the rotary compressor for the purpose of solving the aforesaid problem created in accompaniment with the refrigeration cycle for a car cooler in a rotary system, it has been determined that even when the rotary compressor is used, if parameters for the suction bore area, discharge amount, and the number of vanes are properly selected and combined the self-suppression acts effectively on the refrigerating capacity during the high speed rotation as in the conventional reciprocating compressor, which has been proposed in the specification of Japanese Patent application No. Sho 55-134048.
Also, after study of the general characteristics of compressors in regard to power consumption as well as the volumetric efficiency, it has been found that if the effective suction area is allowed to vary in at least two stages and the effective areas in the first half and the second half in the suction stroke are properly set, then during low speed rotation the drive torque is expected to decrease, and moreover, during high speed rotation sufficient capacity control is obtained, which has been proposed in the specification of Japanese Patent application No. Sho 56-62875.